1. Field of the Invention
The present invention relates to a cooler for cooling both sides (top and bottom surfaces) of a semiconductor device.
2. Description of the Related Art
There is disclosed in JP2001-320005A one of the conventional coolers for cooling both sides of a semiconductor device, which comprises: a plurality of flat cooling tubes each of which has heat-absorbing surfaces for contacting the surfaces of semiconductor modules and one or more channels for passing a coolant and is disposed alternately with the semiconductor module; an inlet header which is connected with one ends of the flat cooling tubes and supplies the flat cooling tube with the coolant; an outlet header which is connected with the other ends of the flat cooling tubes and collects the coolant from the flat cooling tubes; and a pressing mechanism (e.g., bolt and nut) for pressing the flat cooling tubes which hold the semiconductor devices from both sides of the semiconductor device.
Further, there is disclosed in JP6-291223A, 1994, one of conventional heat sinks for dissipating heat from both sides of a semiconductor device.
However, the cooler as disclosed in JP2001-320005A has a disadvantage that the temperature of the semiconductor may vary widely, even when the heat generated by the semiconductor devices is even.
The inventor made clear through research that the temperature variation is caused by a variation of the pressing force on the semiconductor device and the flat cooling tube, because thermal resistance depends upon the pressing force.
The flat cooling tubes are deformed in the direction perpendicular to the semiconductor surface most greatly at the center portion where the bolt and nut press them, while they are deformed least at both ends (inlet and outlet of the coolant), because they are fixed to the headers. As a result, the pressing force varies depending upon the contact positions in the longitudinal direction of the flat cooling tube. Further, the deformation varies due to a dimensional variation such as a variation of affixing positions of the flat cooling tubes to the headers and variation of thickness of the flat cooling tubes. As a result, the pressing force becomes varied. Concretely, some part of the fastening force of the bolt is absorbed for an elastic deformation of one of the flat cooling tubes and the rest becomes the pressing force between the semiconductor device and the flat cooling tube. Hence the variation of the reaction force caused by the elastic deformation results in the above-mentioned pressing force variation.